Pepe went down injured, so Real knocked the ball out of play near the halfway line to allow the defender to receive treatment. When the match restarted, Barcelona returned the ball to Real in the most cynical way possible – thumping it downfield to give José Mourinho's side a throw-in close to the corner flag, then pushing forward to press, boxing Real into the corner.

It was highly unsporting, clearly, but it was also extremely foolish. Real absolutely thrive in those scenarios – dead ball situations close to their own goal, forcing the opposition to concede space behind their defence. Eight Barcelona players were now committed into Real's half and within five seconds Kaká and Karim Benzema were breaking against Barcelona's two centre-backs, the move coming to a premature conclusion with Kaka's miscontrol.

At Porto, Chelsea and Internazionale, Mourinho's sides were always dangerous on the break, but his Real side are even better. The number of opposition corners Real convert into goalscoring chances is extraordinary and, worryingly for Manchester United, Real's 'big-game strategy' seems to work better away from the Bernabéu. Last week's 3-1 victory at Camp Nou was a fine demonstration of that, as was January's 5-0 win at Valencia, where Real completed the scoring before half-time.

Their five league defeats this season have come away against sides who did not attack persistently – Getafe, Sevilla, Betis, Málaga and Granada. Granada did not even manage a shot on target, scoring instead through an early Cristiano Ronaldo own goal, and managed just 28% of possession. But they did not need to attack, so they did not concede.

To stop Real's counterattacks, opponents have realised that they cannot attack with great numbers themselves. Push the full-backs forward and it leaves space for Ronaldo and Angel Di María. Leave gaps in midfield and Mesut Ozil will punish you. Xabi Alonso can switch the play to the required zone with his long diagonals, while Sami Khedira can charge forward into spaces created by Ozil. Only upfront are Real anything short of top-class, where Gonzalo Higuaín has become Mourinho's first-choice centre-forward despite an underwhelming campaign. His movement is clever, though – he makes runs from left to right, dragging the centre-backs out of position to leave Ronaldo running one-on-one at the opposition right-back.

The interesting thing about Sir Alex Ferguson's first-leg strategy was how he mixed an attack-minded starting XI with a very defensive approach. When Robin van Persie, Wayne Rooney, Shinji Kagawa and Danny Welbeck were all named on the teamsheet many expected an end-to-end thriller. Instead, Ferguson had decided Welbeck and Rooney were best suited to the defensive jobs in wide roles, rather than the out-of-form Nani and Antonio Valencia. Kagawa was utilised in the central, counter-attack-prompting role he played brilliantly at Borussia Dortmund, and his hat-trick against Norwich at the weekend might see him given another start.

On paper something similar to the first-leg strategy makes sense: United must defend solidly, yet offer a counter-attacking threat to keep Real from piling forward. A clean sheet would ensure United's progression – but the calibre of Real's attackers suggests they'll probably need to score.

Ferguson will be aware that many of Real's defeats this season have been because of poor set-piece defending, which is unusual for a side managed by Mourinho. Welbeck's opener at the Bernabéu was another example of this weakness, and United have scored 19 league goals from set-pieces this season, more than any other side in Europe's major divisions. Defenders like Patrice Evra and Jonny Evans have been surprisingly prolific, so there's an obvious temptation to throw men forward at corners.

Real's speed on the break, however, means that if they defend the set-piece successfully, United are immediately at risk of conceding.